Optical fiber lasers

A fiber gain medium provided by a rare-earth doped fiber (10) is contained in a first resonant cavity by end reflectors (12, 18). The reflector (12) is wavelength selective to limit the frequency band of the first resonant cavity. The first resonant cavity also contains a second resonant enhancement cavity (16) with multiple transmission bands lying within the first resonant cavity's frequency band. Multiple standing wave modes of the first resonant cavity lie within both the frequency band of the first resonant cavity and the transmission bands of the second resonant cavity, and it is these standing wave modes that support laser action when the rare-earth doped fiber is suitably pumped by pump lasers (40).